Here are the steps to restore your iPhone battery and performance to pre-ios4 luster.
1. You must set your phone to factory defaults: on the iPhone choose Settings, General, Reset (at the bottom), Erase all Content and Settings. Be aware it will take several minutes to reboot as a new phone
2. Attach your iPhone to a computer running iTunes and sync as a new phone without syncing music or contacts.
3. Sync ios4 compatible apps
4. Sync your e-mail, contacts and calendar
5. Sync your music and pictures. This is the final step because it is the most time consuming. I suggest you enjoy a nice hot cup of coffee whilst you wait.